1. Field of the Invention
The present invention generally relates to seatbelt restraint systems for motor vehicles. More particularly, the present invention relates to a linear pretensioner of a seatbelt restraint system in a motor vehicle.
2. Related Technology
Seatbelt restraint systems used for restraining occupants in a motor vehicle seat play an important role in reducing injury to the occupants in the unfortunate event of a vehicle crash. While there are several varieties of seatbelt restraint systems, the conventional “3-point” variety commonly has a lap belt section extending across the pelvis and a shoulder belt section crossing the upper torso of a seated occupant. The lap and shoulder belt sections are each connected to the vehicle structure by anchorages and may be further fastened to each other or formed portions of a continuous length of seatbelt webbing. Seatbelt restraint systems that are manually secured by the occupant (“active” types) also typically include a latch plate attached to the belt webbing. Such a system further includes a seatbelt buckle attached to the vehicle body structure by another anchorage. The latch plate is received by the buckle thereby allowing the seatbelt restraint system to be fastened, enabling restraint, and unfastened, allowing entrance and exit from the vehicle. Of the anchorages securing the lap and shoulder belt sections, one anchorage typically includes a belt retractor to store the belt webbing. This belt retractor may further act to manage belt tension loads during a crash situation. Seatbelt restraint systems, when deployed, effectively restrain the occupant during a collision.
OEM (Original Equipment Manufacturer) vehicle manufacturers often provide seatbelt restraint systems with pretensioning devices. These devices tension the seatbelt either prior to impact of the vehicle (also known as a “prepretensioner”) during a collision or at an early stage of a sensed impact/collision so as to enhance occupant restraint performance This pretensioning takes out slack in the webbing and permits the seatbelt restraint system to engage the occupant early in the crash sequence.
One class of pretensioning devices is a pyrotechnic linear pretensioner (PLP). In one specific implementation, a PLP can be implemented as a pyrotechnic buckle pretensioner (PBP) that is attached to the seatbelt buckle. In another implementation, the PLP can be attached to a webbing guide loop or the anchorages connected to the opposing ends of the seatbelt webbing. Since both of the above types pull a seatbelt system component linearly to apply tension in the seatbelt webbing, both PLPs and PBPs are collectively referred to as PLPs. When a collision occurs, a pyrotechnic charge of the PLP is fired, producing an expanding gas that pressurizes a gas chamber within a tube. This pressure forces a piston to move in the tube. The piston is connected with the belt system by a cable or strap, and the stroking of the piston tightens or “pretensions” the belt against the occupant. Various examples of PLP and PBP designs are provided in U.S. Pat. No. 6,068,664, which is hereby incorporated by reference.
PLPs in accordance with the known design approaches utilize a machined or die cast combustion chamber and a tubular piston cylinder formed of aluminum or steel. The parts are typically threaded or staked together. In addition, there are mounting features formed as part of the combustion chamber or stampings. These mounting features are fastened to the die cast combustion chamber. Although these devices operate satisfactorily, the requirement of die casting or machining a solid metal blank results in a relatively heavy component and requires costly tooling and equipment for production.
Designers of automotive components are constantly striving to reduce the mass of the components as part of the goal of providing higher fuel efficiency for motor vehicles. Additionally, these same designers are also constantly striving to reduce costs in automotive components.